Hi,

I just purchased a new condo for my son. The condo is on the 16th floor (very top floor) and is 805 sq ft with open floor plan - kitchen, living room with wood floors, bedroom, and small bath. The windows face East.

The walls and floors are concrete. The floor covering in the LR is wood, in the kitchen and bathroom it is tile and in the bedroom the floor covering is berber carpet.

When we turn on the AC when the temperature in the unit is 77 with a target temperature of 72, the AC runs constantly for 8 hours and never reaches the target temp of 72 to shut off (it would need to go to 71 to shut off).

How long should an AC run for the temperature to drop 5 degrees? The AC company says it is 1.5 ton. The label on it says it is 10 SEER, the lowest efficiency.

Thanks so much for your response.

Tom

Sounds like it needs to be checked out, shouldn`t take that long to drop 5 degrees,is possible that its undercharged from the factory,is it a through the wall unit? Or is the a/c on the roof ?

You should have no problems cooling 805 sq ft with a 18000 BTU system. I would say something is wrong with the equipment. Dirty --- filter, evaporator coil, condenser coil, low on freon or all of the above.

The unit is located in a closet like room, which is located in one corner of the living room, next to the hot water heater.

Thanks for your help. My wife and I are meeting with the AC Company representatives who installed and designed the system and the builders representatives.

Could it be an under-sized unit?

See what those supposed professionals say first then post back results.

Hi,

Met with representatives of the A/C company and the builder.

It took 3 1/2 hours for the thermostat to go from 78 to below the target of 72 (71.6) for the A/C to finally shut off. The outside temperature at 08:30 was 66.

How long should it take for the temperature go from 78 to 72 (e.g. 71.6)?

Although the drywall around the thermostat had been cut open the previous day and R13 insallation installed because it was felt that the thermostat wasn't going down because of warm air behind the thermostat, the A/C professionas measured the temp behind the thermostat and still felt it was still too high and that warm air was entering the thermostat from behind resulting in it not reaching its target of 72.


Airflow measurements were taken:

Bedroom- Actual 224 cfm, Design 175 cfm
LR - Actual 225 cfm, Design 175
LR - Actual 173 cfm, design 100
Kitchen - Actual 92 cfm, design 100
Bath - Actual 48, design 50

Return temperature = 72.8
Out of register = 54.4
Pressure = 64/230

Freon level was acurate.

temperature behind thermostat = 77.6

It was decided that the thermostat should be set to 70 and left running all weekend to dry out wall, etc (it's a new condo although it has been unoccupied for 1 year). We will meet again on Monday to see if the temperature behind the thermostat is still higher than the room temperature. The A/C company still feels the A/C is functioning properly and the result of the A/C not turning off is because of air intrusion behind the thermostat, even though the wall was insulated with R-13 insallation behind and around the thermostat.

Does all this make sense to anyone, because it doesn't to me.

Any comments, opinions, and suggestions would be very much appreciated because this has been going on for three days and nobody seems to know what to do or what the cause of the problem is.

Please help.

Thanks so much.

Tom

Did they caulk the hole where the wires come through the wall at the thermostat. If they did not it will effect the proper operation of the thermostat. In some cases It has made a big difference in the operation.

Return temperature = 72.8
Out of register = 54.4 18.4 total D

You have a OK TD Total Differential Best is around 20-22

You might have to space that thermostst off the wall to create a air space behind the thermostat if the hot wall situation persists.

It may just be me but the way I look at it the low side of the pressure readings look low for a room return temp of 78 degrees and the high side looks high for a out side temp of 66 degrees. Something is wrong the metering device is restricting the flow of freon or your not moving air and its over charged. The cfm on the intake(return air) looks low all so do you have only one return air for the system?

Hello,

Yes, there is only one air return. It's located near the entrance in the very front part of the living room, the kitchen is to the left, the bathroom is to the right.

The return temp is 72.8, not 78.

Thanks so much. Your comments are very much appreciated since my wife and I will meet with the A/C company reps and the builder reps this Monday, June 9.

It's going to be in the mid 90's here in Alexandria, VA today with a heat index of over 100 so it will be interesting to see how that impacts the operation of the A/C.

Tom

Hi,

The hole where the wires come through the wall was not caulked.

Would a new thermostat from a different manufacturer make any difference?

How long should it take for the temp to go from 78 to 72 degrees and shut off the H/C?

Please keep the comments & suggestions coming. They will be VERY helpful to me when I meet with the A/C company and builder reps this coming Monday, June 9. I will let all of you know what happens then. I know they intend to take a another set of measurements and compare them to the measurements they took yesterday.


Tom

Hi,

I have another question -

Would a new thermostat from a different manufacturer make any difference?

Thanks

The hole where the wires come through the wall was not caulked.

Caulk the hole and you may have to space that thermostat of the wall as mentioned before to get the sensor to detect the correct temperature. (You mentioned hot walls) Concrete is a heat soak material. Is the thermostat on a concrete wall?

NOTE: All there thermostats are not accurate but usually very close in temp readings. Use a good quality thermometer for temp readings.

The time it takes for temp changes is not set in stone. It will be different for different structures.

Use a good Honeywell or White Rodgers thermostat BUT it will not make the unit cool faster just give better control.

Hi,

No, the A/C is fastened to drywall. I find it very hard to believe that air intrusion behind the thermostat is causing improper functioning of the A/C. Especially since R13 insallation was installed inside the wall all around the thermostat.

Today we arrived in the condo (we are currently still residing in a hotel) at 12:45. The temperature outside was 85 going to 95.

The thermostat was set to 70 the day before. When we arrived at 12:45 PM the inside temperature was 71.3. After we had been there for only a few minutes the temperature proceeded to rise to 72.9 by 1:45 PM (an hour later). The temperature continued to rise to 74.9 at 5:45 PM. At 6:30 PM it was 74 degrees.

My son and I were putting together furniture and I was sweating!

I am so frustrated about this A/C problem. The A/C is still under warranty and I want to ask the A/C rep to install a new A/C when we meet with them on Monday. Does that seem unreasonable to you?

What would you ask for or do if you were me? I really need your professional advice. Please help.

Thanks and have a nice Sunday.

Tom White

If I were buying the place I would first ask for it to be repaired or replaced with a larger unit if necessary. If the repairs/ larger unit fail then I would call another company and get there opinion on the problem.

Document all conversations/discussions. Keep track of time spent on the problem etc. If you have not closed or paid for the unit I would find a way to with hold $$ to force the issue but you have to allow time for them to fix the situation first.

Not much else that can be done here. Let us know how it all turns out. Good luck.

Good Morning,

Thanks very much for your recommendations, suggestions, and comments. They were truly appreciated.

Tomorrow, when we meet with the builder and A/C reps, I will ask for a replacement unit. I'll keep you informed about this continuing saga.

Thanks again. Your advice and recommendations are invaluable to an inexperienced person like me.

Tom White

Hi,

I have one last question.

If it becomes necessary, who should I hire to provide a second opinion - should I hire an A/C Company, a Mechanical Engineer, or??


Thanks again.

Tom

That is a toss up. Naturally a Mechanical Engineer would be best but they can cost $$$$$. They usually have a PE stamp for the state they work in and usually what they say is considered the last word on a subject. At least that is the way it works in a court of law here. I am considered a PW (professional witness) in the USA. I used to travel to different states taking the stand to testify after my inspections of the problem. I do not do that any more and it is also expensive.

I believe the problem could be isolated to a unit not performing to the manufactures specifications,improper install or anything to do with improper refrigerant charging and refrigerant flow problems. (improper metering device,kinked refrigerant lines,)etc.

T-Top mentioned this in his post in regards to the temp/pressures of the unit at a given temperature not sounding correct and he is right in that statement.

Since this is a condo and I am sure there are more just like it in the building. Have you talked to the neighbors about how well there unit works? This info may also be of use to you.

No one likes to be uncomfortable especially when they paid good money for the comfort to start with. Good hunting.

HVAC1000,

We have spoken to two other residents one on the 16th floor (same floor as ours) and one who lives on the third floor. They both say that they do not have a problem with their units.

I appreciate your advice and will use your information as points for replacing the unit.

Thanks and have a nice day.

Tom White

I am sure the next few days will be interesting for you. Good luck.

HVAC1000,

Just one last question.

From your comments and suggestions seem to say that you do not agree that the problem with the A/C operation is caused by air intrusion behind the wall of the thermostat. Is my inference correct?

Thanks and I won't bother you any more. You have been very, very helpful.

Tom